Device for inspecting an interference filter for a projection television display tube.

摘要

In a device for measuring the cut-off wavelength of an interference filter (30) for a projection television display tube, the interference filter (30) and a bandpass filter (42, 43) are arranged one behind the other. The bandpass filter has a transmission characteristic with a cut-off wavelength which approximately coincides with the desired cut-off wavelength of the interference filter, but with a slope varying in the other direction. A white light beam generated in a light source (40) is incident through the two filters. The intensity which is measured by a detector (52, 53) on the other side of the filters is a measure of the cut-off wavelength of the interference filter (30). The device may have a second measuring system (41, 51) for measuring the absorption in the interference filter.